1. Field of the Invention
This invention relates to thin film magnetic write head fabrication in general and, more specifically, to a method of improving the magnetization pattern of such a write head by forming it with a wider trailing pole than leading pole.
2. Description of the Related Art
Thin film magnetic write heads are used to encode magnetically stored information on moving magnetic media such as tapes and discs. In the simplest terms, such a head consists of two pole pieces separated at the air-bearing surface (ABS) by a narrow gap (the write gap) and yoked together behind the ABS to form an approximately horseshoe-shaped assembly. A conductive coil is patterned between the pole pieces which, when electrically energized, induces a magnetic field between the poles which fringes across the gap. It is this induced field that encodes small magnetic regions in the moving medium.
The rapid changes in the state of the art have necessitated continual improvements in the area density of information that can be magnetically encoded and decoded in the moving medium. For a disk, this area density is a product of the number of recording tracks per mm measured radially, and the number of flux reversals per mm along the track, measured tangentially. With the development of the extremely sensitive magneto-resistive read heads, methods for improving the area density are now focussing on extending the limits of the inductive writing technology.
There are several approaches to improving the writing technology, one of which is to narrow track widths and thereby increase the number of tracks per mm. As the tracks become narrower, however, it is increasingly necessary that the magnetization pattern on the track be sharply bounded and well defined. This not only insures maximum readability of each track, but it also reduces the interference between adjacent tracks. This approach requires that the writing tip of the magnetic pole assembly, including its write gap, be made as narrow as possible. In addition, the fringing fields extending beyond the width of the write gap should be minimized so that writing does not also occur on portions of the recording media away from the selected track. In the prior art, such fringe field minimization has generally been attained by forming the write gap within a narrow, symmetric pole piece. One way of forming such narrow, symmetric pole pieces and write gaps is to first form them with a relatively wide shape and then trim the shape to the desired width by means of an etching process, which, typically is a series of ion-beam etches (IBE) or milling process. These etching processes are time consuming and lead to undesirable width discontinuities between various portions of the pole piece. Such a prior art method of producing a symmetric, trimmed upper pole piece is taught by Chen et al. (U.S. Pat. No. 6,243,939).
Armstrong et al. (U.S. Pat. No. 5,901,432) teach a method of trimming a pole piece wherein the WG layer of nickel phosphorus is initially formed to the correct thickness by electroplating it within a photoresist form. Thus, the ion-beam milling is not required to remove any of the WG layer since it is already of the correct dimensions.
Koshikawa et al. (U.S. Pat. No. 6,199,267) teach a method of forming a magnetic write head with an ion-beam trimmed pole piece, in which unwanted side-effects of the ion-beam are eliminated by forming depressions to either side of the pole piece and filling them with non-magnetic material.
Tran et al. (U.S. Pat. No. 5,578,342) teach a method of forming a write head whose leading and trailing pole pieces have substantially the same width and whose edges are aligned. The purpose of this width uniformity is to eliminate data transitions that are written wider by the trailing pole (trailing relative to the motion of the medium being written on) than by the leading pole, thus leading to poorly defined track edges (“transition curvature”).
The present invention was motivated by the realization that a track magnetization pattern can be improved by forming the write head with a slightly wider trailing pole than leading pole. The prior art cited above does not address the advantages of such a write head or teach a method of pole trimming that would be suitable for forming it. In a related patent application, Ser. No. 10/284,848, filing date Oct. 31, 2002, now issued as U.S. Pat. No. 6,887,355, fully incorporated herein by reference, a pole trimming method is taught that allows the efficient formation of a write head having leading and trailing poles of equal and uniform width. That method can now be used to form a write head in which the leading pole edge is narrower than the trailing pole edge.